[1] Univ Ft Hare, Dept Chem, Alice, South Africa
[2] Tshwane Univ Technol, Dept Chem Met & Mat Engn, Pretoria, South Africa
[3] CSIR, DST CSIR Natl Ctr Nanostruct Mat, ZA-0001 Pretoria, South Africa
[4] Univ Johannesburg, Dept Appl Chem, ZA-2028 Johannesburg, South Africa